In the hydrometallurgical industry, it is of common practice to refine metal by electrolysis in electrolytic cells especially designed for this purpose. The metals to be refined are usually conventional metals such as copper, zinc, nickel or cadmium, or precious metals such as silver, platinum or gold, and others.
It is also of common practice to use metal plates as anodes or cathodes or both. These metal plates often weight several hundred pounds. Usually, the metal to be refined, or the metal used to carry the electric current, is in the form of plates of a given thickness, which are provided at their upper end with two laterally extending projections, called hanging bars. Such projections facilitate gripping, handling and hanging of the plates on lateral sidewalls of the cells. These projections also serve to electrically contact or insulate the electrode.
In use, the plates which, as mentioned, can each weight several hundred pounds, are immersed into the cells in parallel relationship and are used as anodes, cathodes or both, depending on the affinity of the metal being refined.
In order to have the electrodes positioned in a precise desired location, it is of common practice to place a member called a “capping board” or a “bus bar insulator” onto the top surface of each lateral sidewall of the cells. These capping boards are used to position the plates with respect to each other. They are also used as electric insulators between adjacent cells and/or the electrodes and/or the ground.
In practice, the capping boards are used not only as supports to position the electrodes, but also as supports to avoid damage to the masonry, concrete or polymer-concrete forming the lateral side walls of the cells during the insertion and removal of the heaving electrodes. They are also used for electrolytic refining and electrowinning of metals.
As examples of such capping boards and the way they can be manufactured, reference can be made to U.S. Pat. No. 4,213,842 and Canadian patent No. 1,102,737 . Reference can also be made to the U.S. Pat. No. 5,645,701 and Canadian patent No. 2,171,412.
The above-mentioned insulating capping boards are used to hold the electrodes at very precise positions. They are also used in combination with electrically conductive contact bars the purpose of which is to allow electrical connection between the ends of the anodes and cathodes located in adjacent cells. Thus, the combined use of capping boards and contact bars has the particularity of allowing both insulation and distribution of electric current.
To achieve proper electrical contact with the contact bar, the plates forming the electrodes are provided with support hanging legs externally projecting on their opposite upper ends. Only one end of the legs of each plate is in contact with a contact bar on one side of the cell where it is located. The other leg of the same plate is held onto the capping board located on the opposite side of the cell in such a way as to be insulated. Thus, the capping board per se plays the role of an insulator and is thus made of insulating material. The contact bar usually extends over the full length of the corresponding capping board in order to connect altogether all the anodes of one cell to all the cathodes of the adjacent cell and vice versa. The contact bar may interconnect all of the cathodes to the anodes on other adjacent cells or perform other electric connection function between electrodes as desired.
There are a few known types of contact bar, each of which has disadvantages and associated challenges.
One typical type of contact bar is of triangular cross-section. The triangular contact bar sits within a seat of a capping board and has three edges and three surfaces which can be sequentially used to provide the electrical connection. The triangular contact bar can thus essentially be used three times, through changing the orientation, which is quite onerous. It contacts the insulator in such a way that causes little compression on the insulator supporting the load of the contact bars and electrodes. However, the electric contact quality is mediocre and can rapidly decrease due to marks, holes and bumps that it may receive on the edge during manipulation of the electrodes. The electrical contact is also substantially linear and thus when the contact bar becomes even slightly warped or bumpy, the quality of electrical contact becomes very poor because of decreased surface contact. This poor contact situation also generates heat which over time damages the insulator. Such heat generation decreases electric current efficiencies and increases operating costs.
Another type is the rectangular or trapezoidal contact bar, which is similar to the triangular contact bar but has a generally rectangular cross-section which rounded corners and a moderately curvilinear side (as seen in FIG. 4, Prior Art). This type of contact bar can be used two times. Like the triangular contact bars, the rectangular contact bars causes little compression on the insulator supporting the load of the contact bars and electrodes, but has similar problems and disadvantages as the triangular type as discussed above.
Another type is the so-called “spool” contact bar which is described is U.S. Pat. No. 4,035,280 (as seen also in FIGS. 1 to 3, Prior Art). The spool contact bar can be used multiple times before changing it and provides excellent electrical contact. To maintain good electrical contact, the spool can simply be rotated. To prevent it from displacing or rolling, it must be retained often by using a V-shaped or notched piece and the retention systems are often complicated and result in certain disadvantages. The spool contact bar may lie on and contact a notched portion of header bars and the weight of the electrodes ensures high pressure contact between the notched header bars and points located on the sidewalls of the spool contact bar. However, the high pressure results in premature wearing and damage to the insulators and replacing insulators is very costly and onerous.
Another type is the so-called “dog bone” contact bar, which has an elongated plate like portion with parallel elevated projections along the length of the contact bar. Some so-called dog bones are continuous and/or have a series of teeth-like projections running along either edge of the plate portion. This kind of contact bar has advantages in terms of handling the electrodes, due to symmetrical hanging legs of the electrodes. This contact system also has similar disadvantages as the triangular contact bar, i.e. wearing, notching and corroding of the triangle edge of the contact and has other disadvantages such as accumulating acid mist which creates corrosion of the contact bar and the insulator. Replacement of the so-called ‘dog bone’ is very difficult and it is also costly to manufacture and has other disadvantages.
There is indeed a need in the industry for a contact bar and capping board technology that would overcome at least some of the aforementioned disadvantages and challenges.